Seasonal rhythms in mental health: a narrative scoping review of neurobiological mechanisms and therapeutic interventions

Seasonal variations in mental health represent a complex interplay between environmental photoperiod changes and neurobiological rhythms, affecting millions globally through conditions like seasonal affective disorder and bipolar seasonality. This narrative scoping review synthesizes current understanding of molecular and neural mechanisms underlying seasonal mental health fluctuations, from circadian clock gene regulation to neurotransmitter system adaptations. The suprachiasmatic nucleus orchestrates seasonal responses through melatonin-mediated pathways, while serotonergic and dopaminergic systems show pronounced seasonal variations correlating with mood and cognitive changes. Brain regions including the hippocampus, prefrontal cortex, and limbic structures demonstrate seasonal plasticity in structure and function. Light therapy (10,000 lux for 30 minutes daily) remains the primary evidence- based intervention, with response typically emerging within 1–2 weeks. Combination approaches incorporating cognitive-behavioral therapy, sleep schedule optimization, and pharmacological interventions are under investigation, though optimal protocols require validation. Emerging research explores personalized medicine strategies based on genetic polymorphisms and chronotype assessment, though clinical implementation awaits rigorous validation. Critical research gaps include biomarker validation for treatment selection, standardized neuroimaging protocols, and translational validation of precision chronotherapy approaches. Future directions prioritize large-scale longitudinal investigations and evidence-based personalization strategies addressing the growing burden of seasonal mood disorders.